C to C+ to C++
Yeah, C++ at one point was a C deriviative, but nowadays they're distinct languages with distinct syntax. There is no C+, only C and C++. For the most part, you could write something in C and it would compile in C++, but there are some tricky cases.
So, many trivial C programs are valid C++ programs, but it's still a subset.
“Ooo, can I call you Señorita Bee?” ~Chibi-Matoran